The noncollinear spin textures provide promising avenues to stabilize exotic magnetic phases and excitations. They have attracted vast attention in the past decades due to their nontrivial band topology. Distinct from the conventional route of involving the Dzyaloshinskii-Moriya interaction in a honeycomb magnet, the interplay of bond-dependent Kitaev and $\mathrm{\Gamma }$ interactions, originating from the spin-orbit coupling and octahedra crystal field in real materials, has demonstrated to be another source to generate noncollinear spin textures with multiple spins in a magnetic unit cell. Notably, earlier works have revealed a triple-meron crystal (TmX) consisting of 18 spins in the frustrated Kitaev-$\mathrm{\Gamma }$ model. Aligning with previous efforts, here we attempt to identify that the TmX hosts several peculiar features with the help of the linear spin-wave theory. To begin with, the symmetric anisotropic exchanges are beneficial for the existence of nonreciprocal magnons, which are stabilized by an external magnetic field. Further, within the regime of TmX, successive topological phase transitions occur, accompanied by the changes of Chern number in value and thermal Hall conductivity in sign. In addition, the topological nature of magnons is also verified by the onset of chiral edge modes in a nanoribbon geometry. Our findings pave the way to study topological phenomena of noncollinear spin textures in potential Kitaev materials.

中文翻译：

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非共线自旋纹理中的拓扑相变和热霍尔效应

非共线自旋纹理为稳定奇异磁相和激发提供了有希望的途径。由于其非平凡的带拓扑结构，它们在过去几十年中引起了广泛的关注。与蜂窝磁体中涉及 Dzyaloshinskii-Moriya 相互作用的传统途径不同，键依赖性 Kitaev 和$\mathrm{\gamma }$源自实际材料中的自旋轨道耦合和八面体晶体场的相互作用已被证明是在磁性晶胞中产生具有多个自旋的非共线自旋纹理的另一个来源。值得注意的是，早期的工作揭示了沮丧的基塔耶夫体内有一个由 18 个自旋组成的三聚体晶体（TmX）——$\mathrm{\gamma }$模型。与之前的工作相一致，我们尝试借助线性自旋波理论来确定 TmX 具有几个独特的特征。首先，对称各向异性交换有利于不可逆磁振子的存在，该磁振子通过外部磁场稳定。此外，在 TmX 范围内，发生连续的拓扑相变，伴随着陈数值和热霍尔电导率符号的变化。此外，磁振子的拓扑性质也通过纳米带几何结构中手性边缘模式的出现得到了验证。我们的发现为研究潜在基塔耶夫材料中非共线自旋纹理的拓扑现象铺平了道路。